The present invention relates to a device for detecting slag flowing with molten metal through an outlet opening in a metallurgical vessel. More particularly, the present invention relates to such a device including a sensor positioned in the area of a metal base plate or outer shell or housing of the metallurgical vessel. The base plate has therethrough a discharge aperture, and the sensor is positioned such that it surrounds the discharged stream of molten metal without making contact therewith. The sensor is of the type including a sending coil and a receiving coil associated with a reference coil.
This type of device is disclosed in DE-OS No. 34 39 369, wherein the sensor is built into the nozzle brick or the brick lining of the metallurgical vessel. Because of high signal amplitude as well as a high signal-interference ratio, this sensor makes it possible to discern and indicate very small proportions of slag in the flowing stream of molten metal, without having to remove the shield that protects the stream of molten metal or hindering a casting operation involving the discharge of molten metal.
However, one disadvantage of this known device results from the position of the sensor in the nozzle brick or the brick lining of the vessel. Thus, these elements of the vessel must be changed frequently. This however makes it impossible to reuse the sensor, even though the sensor itself still probably is operable.
Furthermore, if the sensor is positioned on or in the base plate of the metallurgical vessel, the signal amplitudes are sharply reduced by the metal shield and by the metal base of the vessel. In addition, with this arrangement the temperature changes of the ferromagnetic metal components in the vicinity of the sensor alter the permeability of the components of the sensor. This results in the generation of strong signal drifts, which could simulate the occurence of slag in the stream of molten metal.